Silos used in processing foods for human consumption are usually thought of as enclosed cylindrical towers for preventing air and moisture from passing in or out of the food stored therein, and in sanitary silos, which are commonly filled from their bottoms, there is often a problem of overfilling the silos causing their rupture.
In an attempt to remedy this problem, an overflow pipe is often installed vertically between the dome of the silo and a sanitary enclosure at the silo's base thereby providing a passageway for discharging the overfilled portion of the silo's content while preserving the silo's sanitary environment by preventing unclean matter from entering the silo through the outlet end of the overflow pipe.
However, because sanitary silos and their vertical overflow pipes often extend nearly 80 feet high, the internal forces exerted by several hundred tons of fluids contained therein are extremely great, especially when the silo is overfilled and the overfilled portion of the fluid enters the inlet end of the overflow pipe and begins its long decent down said pipe to its outlet end thereby initiating the siphonal discharge of the overfilled portion in the silo.
Although the principle of a siphon is well known, it shall briefly be repeated here as it relates to the present problem with sanitary silos.
It has long been known that the surfaces of two fluids will always attempt to attain the same level provided that there is a common connection between them. If, for example, the surface of one fluid is higher than another, a siphonal discharge of the higher fluid to the lower may be accomplished through a tubular conduit called a siphon. Because the pressure of the fluid at the higher end of the siphon tube is greater than the pressure at the lower end of the siphon tube, fluid will be pulled down the siphon tube by gravity until the pressure at both ends of the siphon tube are equal as demonstrated when the surfaces of both fluid levels are at the same height and therefore both sides of the siphon tube contain the same weight of fluid causing the siphon to stop.
In sanitary silos, however, there is usually only one essentially vertical overflow pipe with its inlet end entering the silo a few feet below the silo's dome which allows a headspace of sanitary atmospheric pressure above food normally stored therein. But when the silo is overfilled the atmosphere in the headspace is quickly replaced with fluid until the overflow pipe can remove it. Once the overflow pipe is full of effluent discharge from the dome there is established the required common connection between the greater pressure at the inlet end and lesser pressure at the outlet end resulting in a downward suctional acceleration of the overfilled portion thereby causing a vacuum in the head-space of the silo's dome.
One logical solution to the problem of suctional discharge in the overflow pipe would appear to be installation of some sort of siphon venting or vacuum breaking device on either the overflow pipe or in the silo's dome, however all such known devices do not address the requirement for sanitation as established by such organizations as the United States Department of Agriculture which require that air vents shall be designed to protect against entrance of foreign material into the silo.
For example, there are known in the prior art numerous siphon venting and vacuum breaking devices generally found in the United States Patent Classification, Class 137, Fluid Handling. Such mechanical devices, like those found in Sub-class 143, are responsive to-and are activated by pressure differences in an enclosed container such as a tank, pipe or conduit but these devices require some mechanical component inside the container in direct or proximal contact with the fluid therein or expose the fluid food supply to the open atmosphere causing contamination.
Accordingly, it is the general object of the present invention to provide an external means with no moving parts which automatically provides sanitary air by suction into a siphonal discharge from an overfilled sanitary silo thereby offsetting and relieving vacuum in the silo's dome to prevent its collapse by implosion.